1. Field of the Invention
This invention relates to a method for making a hermetic ceramic to metal seal. More particularly, an optically transparent ceramic lens is press-fit into an aperture formed in a metallic housing and a metallic coating layer then deposited on the aperture walls.
2. Description of Related Art
Hybrid electronic packages that incorporate an optical or opto-electronic component typically include a lens for receiving photonic signals and metallic leads for receiving electrical signals. To maintain the integrity of circuitry contained within the hybrid package, the package is hermetically sealed.
In the manufacture of one type of hybrid package, each metallic lead is surrounded by a glass bead and the assembly is inserted into an aperture extending through a metallic housing. When heated to above about 800.degree. C., the glass melts and fuses to both the lead and the housing forming a hermetic glass to metal seal that also electrically isolates the leads from the housing.
For optical devices, a lens is included. The lens is formed from an optically transparent glass or ceramic and is coated with an anti-reflective coating. To maintain the effectiveness of the anti-reflective coating, the lens cannot be exposed to temperatures above about 500.degree. C. This temperature exposure limitation prevents the lens from being joined to the hybrid package housing by a conventional glass to metal seal.
U.S. Pat. No. 5,177,806 to Abbott et al., that is incorporated by reference in its entirety herein, discloses that optical fibers have been bonded with metallic solders and epoxy resins. While both metallic solders and epoxy resins may be applied at temperatures well below 500.degree. C., the hermeticity of hybrid packages using these sealants is suspect and not adequate for the housing of complex integrated circuits.
There remains, therefore, a need for a method to make a ceramic to metal seal such that an optically transparent lens can be joined to a metallic housing that meets the dual objectives of an assembly temperature of less than 500.degree. C. and hermeticity acceptable for integrated circuit packages.